Halide perovskites, such as CsPbI3, are well-known as semiconductors for optoelectronic applications. However, this diverse family of compounds can also exhibit a range of unexplored physical properties, including those of quantum materials. We conducted a quantum mechanical study of CsTiI3 to investigate its potential as a quantum material. Our calculations reveal complex magnetic interactions that are highly tunable by external pressure. We found that CsTiI3 undergoes a series of pressure-induced phase transitions: from a linear-chain ferromagnetic (FM) half-metal to an antiferromagnetic (AFM) metal at 6.5 GPa. At even higher pressures, the titanium (Ti) magnetic moment is quenched, leading to a transition to a non-magnetic (NM) metallic state. The ferromagnetic to antiferromagnetic phase transition is explained by the 90 degrees superexchange model, where the behavior of the intrachain magnetic coupling is governed by the value of the angle within the I-Ti-I chain. This discovery of pressure-tunable magnetism in CsTiI3 highlights the unexplored potential of halide perovskites for novel quantum phenomena.

Superconductivity in noncentrosymmetric RPt2Si2 (R = rare earth) compounds exhibit a rich playground to explore the competition between different ground states, such as unconventional superconductivity, antiferromagnetism and charge density wave. Here, we report the successful single crystal synthesis of noncentrosymmetric YPt2Si2 superconductor, with a transition temperature Tc = 1.67 K, via Sn flux method. The high quality of the prepared single crystals was confirmed using powder and Laue XRD measurements. The superconducting and normal state properties are investigated using electrical transport and heat capacity measurements down to 0.5 K. In the normal state, unlike LaPt2Si2, no charge density wave transition is observed in YPt2Si2, as evidenced by electrical transport and specific heat measurements. A relatively large Kadowaki-Woods ratio and a linear temperature variation of the electrical resistivity in an extended temperature range of 50-300 K suggest an unconventional normal-state in YPt2Si2. The estimated superconducting parameters indicate that YPt2Si2 is a type-II superconductor with weak electron-phonon coupling. The temperature dependence of specific heat in the superconducting state can be explained reasonably well using an isotropic two-gap model. A positive curvature near Tc in the temperature variation of upper critical field also supports the two-gap superconductivity. First-principles DFT calculations suggest a BCS-like superconducting state driven primarily by d-electron contributions. The calculated electron-phonon coupling constant identifies the material as a weak-coupling superconductor, with the McMillan-Allen-Dynes formula yielding a Tc of 1.8 K. Additionally, we provide a comparative analysis of the superconducting and normal-state properties of YPt2Si2 and compositionally similar LaPt2Si2.

A comprehensive first-principles investigation of the structural, stability, electronic, and optical properties of the copper-based chalcogenides CuNbS3 and CuTaS3 is presented in order to assess their potential for solar-cell applications. The most stable crystal structure of each compound was identified by fitting the total energy to the Birch-Murnaghan equation of state. Phonon dispersion calculations confirmed the absence of imaginary frequencies throughout the irreducible Brillouin zone, demonstrating the dynamical stability of both compounds. Electronic-structure calculations using the PBEsol and r2SCAN exchange-correlation functionals indicate that both materials are indirect-gap semiconductors with band gaps below 1 eV. To overcome the well-known underestimation of semilocal functionals, quasiparticle corrections were evaluated within the G0W0 approximation, yielding indirect band gaps of 1.04 eV for CuNbS3 and 1.09 eV for CuTaS3. The influence of electron-hole interactions on the optical response was further examined by solving the Bethe-Salpeter equation. The resulting spectra reveal strong absorption in the visible range, supporting the potential of both compounds for photovoltaic and optoelectronic applications.

NaAgO is investigated as a potential top-cell material for tandem solar cell configurations. To assess its suitability, the structural, bonding, and electronic properties of this semiconductor are examined using density functional theory with the PBEsol exchange-correlation functional and the GW approximation. The material crystallizes in an orthorhombic crystal structure (Ibam space group) and exhibits polar covalent bonding with a bulk modulus of 67.4 GPa. NaAg3O2 is found to be a direct (at Gamma) semiconductor with a bandgap of 1.79 eV. The calculated dielectric and optical properties show that NaAgO is transparent to low-energy photons but exhibits a sharp increase in light absorption near its bandgap of 1.79 eV, reaching absorption coefficient as high as cm, motivating experimental synthesis and further investigation. The bandgap, combined with its bonding and optical characteristics, suggests its potential as a top-cell material in tandem solar cell configurations.

Cs2AgSbCl6 double perovskite (DP) has been synthesized through many solid-state and solution routes.

We report the magnetic properties of the Y-doped GdNiSi3 intermetallic compound, prepared by Sn-flux method and investigated by susceptibility, magnetization and heat capacity measurements. The results indicate that the antiferromagnetic structure of GdNiSi3 is altered by Y concentration allowing that the coexistence between antiferromagnetic/ferrimagnetic state takes place under slight changes in the strong RKKY interaction. This is confirmed by supercell first-principles calculations using Density Functional Theory along with a Hubbard U parameter (DFT+U). The emerging ferrimagnetic order creates the necessary conditions for the existence of strong exchange anisotropy interaction responsible by the exchange bias effect in Gd0.50Y0.50NiSi3 and Gd0.35Y0.65NiSi3 single crystal

At present, efforts are being made to find new low-cost materials for photovoltaic, optoelectronic and energy storage applications. In this regard, compounds of the halide perovskite type have been increasingly studied over the past few years. The incorporation of small cations in these compounds and their possible use in rechargeable batteries can be achieved by the electrochemical reversibility technique, where perovskites with large cations are used to obtain a new isostructural compound with smaller cations and large interstitial space or free vacancies for ionic transport. The present work studied the electrochemical reversibility of lithium-ion into CH 3 NH 3 NiCl 3 (MANiCl 3 ) active material, after the formation of MA + vacancies or interstitial spaces, taking both experimental and theoretical approaches. The material displayed an anodic behavior and an initial capacity of discharge of ca. 170 mAhg- 1 at 0.2C (0.1 mA), a full capacity retention up to the first 25 cycles of charge - discharge, and even reached a retention of up to 80 % of initial capacity at the 80th cycle. First-principles density functional theory calculations show that the shape of the crystal lattice and volume changes of all the different phases involved in the electrochemical process are tiny, at about 3 & Aring; 3 per cell. In addition, there are no appreciable elastic contributions to the energy variation during the de-lithiation/lithiation process, indicating that memory effects are not an issue. The calculated formation energies of the lithiated structures and the open circuit voltages are-2.91 eV and 1.33 V for Li n MA 1-n NiCl 3 and-1.41 eV and 2.91 V for Li 2n MA 1-n NiCl 3 , respectively. These findings suggest that incorporating one or, at most, to two lithium atoms is favorable for the overall stability and electrochemical performance.

Through systematic study of the passivation of the CH 3 NH 3 PbI 3 surface with different ammonium molecules, we introduce the concept of the Supramolecular Virtual Crystal (SVC) and propose a novel method to design the molecular passivation of the HOIP surface.

There is an ongoing effort to replace rare and expensive noble-element catalysts with more abundant and less expensive transition metal oxides. With this goal in mind, the intrinsic defects of a rhombohedral perovskite-like structure of LaMnO3 and their implications on CO catalytic properties were studied. Surface thermodynamic stability as a function of pressure (P) and temperature (T) were calculated to find the most stable surface under reaction conditions (P=0.2 atm, T=323 K to 673 K). Crystallographic planes (100), (111), (110), and (211) were evaluated and it was found that (110) with MnO2 termination was the most stable under reaction conditions. Adsorption energies of O2 and CO on (110) as well as the effect of intrinsic defects such as Mn and O vacancies were also calculated. It was found that O vacancies favor the interaction of CO on the surface, whereas Mn vacancies can favor the formation of carbonate species.

Cu2MnSnS4 shares several promising properties with the widely investigated Cu2ZnSnS4 for photovoltaic applications such as containing only earth abundant and non‐toxic elements, and suitable absorption characteristics for absorber materials. Thin film Cu2MnSnS4 samples with various cation compositions are co‐sputtered reactively followed by a high temperature anneal. Formation of Cu2MnSnS4 and co‐existence of several secondary phases is verified by XRD and Raman. Our investigation of the crystal structure based on first‐principles DFT confirms that stannite crystal structure is preferred over kesterite, although, further verification considering cation disorder is needed. The direct band gap of Cu2MnSnS4 is calculated as 1.52 eV (1.62 eV) for stannite (kesterite), which coincides with the range of the measured band gaps from spectrophotometry of 1.42–1.59 eV. After further annealing treatments below 240 °C, the absorption shows reversible changes: the band gap blue‐shifts and the Urbach tail energy is reduced. It is concluded that, just like Cu2ZnSnS4, disorder also occurs in Cu2MnSnS4. The implications of our findings are discussed and related to the current understanding of cation disorder in Cu2ZnSnS4 and related compounds. Furthermore, for the first time first‐principles DFT investigations are presented for the thiospinel Cu2MnSn3S8 which is observed experimentally as a secondary phase in Sn‐rich Cu2MnSnS4 thin films.

Piezoelectric materials are widely used in electronic devices and, traditionally, various lead-based materials have been implemented in such applications. However, because of the damage caused by lead, other materials with similar characteristics that do not cause a negative impact on human health and the environment have been developed. A material with those characteristics is potassium-sodium niobite K0.5Na0.5 Nbo3. In this study, we investigate the thermogravimetric, structural, and microstructural properties of powders of such system obtained through oxide mixing with the aim of establishing the effect and efficiency of grinding (using a horizontal and a planetary ball mill grinder) on the production of the final material. It was determined that horizontal grinding and calcination at 900°C create the optimal conditions for obtaining K0.5Na0.5 Nbo3 powders, by oxide mixing, with the adequate structure and microstructure to continue the densification and/or doping processes.

We report the discovery of bulk superconductivity in the ternary intermetallics YNiSi3 and LuNiSi3. High-quality single crystals were grown via the Sn-flux method and studied using magnetization, specific-heat, and resistivity measurements at low temperatures. The critical temperatures obtained from these different techniques are in very good agreement and yield T-c = 1.36(3) K and T-c = 1.61(2) K for YNiSi3 and LuNiSi3, respectively. Magnetization measurements indicate that both compounds are among the rare cases where type-I superconductivity occurs in a ternary intermetallic, however, the jump in the specific heat at the transition is lower than the value expected from BCS theory (Delta C-el/gamma T-n(c) = 1.43) in both materials and is equal to 1.14(9) and 0.71(5) for the Y and Lu compounds, respectively. Resistivity measurements exhibit sharp transitions but with critical fields mu H-0(c)(0) (approximate to 0.05 T for YNiSi3 and approximate to 0.08 T for LuNiSi3) considerably higher than those obtained from the magnetization and specific heat (approximate to 0.01 T). First-principles density functional theory calculated electronic structure shows that these compounds have highly anisotropic and complex Fermi surfaces with one electronic and two holelike branches. One hole branch and the electron branch have a large cylindrical topology connecting the first Brillouin-zone boundaries, the former being built up by the hybridization of Y(Lu) d, Ni d, and Si p states, and the latter being built up by Ni d and Si p states. The calculated phononic structures indicate that the coupling of the Y(Lu), Ni d, and Si p electrons in the low-lying optical phonon branches is responsible for the formation of Cooper pairs and the observed superconducting state. Therefore, these compounds can be classified as anisotropic three-dimensional metals with multiband superconducting ground states in the weak-coupling regime.

IrGa3 is an intermetallic compound which is expected to be a metal, but a study on the electronic properties of this material to confirm its metallic character is not available in the literature. In this work, we report for the first time a first-principles density functional theory and semiclassical Boltzmann theory study of the structural, electronic and transport properties of this material. The inclusion of the spin-orbit coupling term is crucial to calculate accurately the electronic properties of this compound. We have established that IrGa3 is an indirect semiconductor with a narrow gap of 0.07 eV. From semiclassical Boltzmann transport theory, it is inferred that this material, with the appropriate hole concentration, could have a thermoelectric figure of merit at room temperature comparable to other intermetallic compounds such as FeGa3, though the transport properties of IrGa3 are highly anisotropic.

Tantalia (Ta2O5) is an interesting material which is used in several technological applications. In particular, this wide gap semiconductor is used as a new material for memristive devices, which could provide a paradigm shift on the memory devices fabrication. These new devices would be faster, denser and less power consuming than those available today. Because of this, we present a study of the optical and dielectric properties of beta-Ta2O5 polymorph by means of first-principles Density Functional Theory calculations. Taking as a starting point the Nashed's model of the crystal structure of beta-Ta2O5 and the generalized gradient approximation (GGA-PBEsol), we calculated the equation of state (EOS) of this polymorph. From EOS we identify the equilibrium volume and for this we calculated the frequency dependent dielectric tensor, refractive index (n = 2.63), absorption coefficient and transmittance. Also, we calculated the electronic (epsilon(infinity) = 6.98) and ionic contribution (epsilon(0) = 43.51) to static dielectric constant and it was compared with some reported values in the literature.

In this work, we have synthesized and fabricated solar cells with the hybrid metal halide compounds with the general formula ABX3, where the A cation is methylammonium, the B cation is nickel, and the X anion is chlorine or a mixture of chlorine and iodine. We obtained experimental evidence that this material is a semiconductor with an orthorhombic crystalline structure which pertains to the space group Cmcm. The bandgap can be modulated from 1.4 eV to 1.0 eV by changing the chlorine anion to iodine. Therefore, we were able to obtain solar cells with efficiencies up to 0.16% with the CH3NH3NiCl2I composition. We have also studied by means of first-principles calculations, taking into account van der Waals dispersive forces, the ground state properties of these materials such as their crystal structure and formation and decomposition energies. We have found that these energies are lowered by the lighter mass anion, and the calculated decomposition energies show that only CH3NH3NiCl3 is stable with respect to the most probable decomposition pathway. The electronic band structure and band edge alignments have been calculated using quasiparticle effects through the GW0 approximation; these materials show an indirect bandgap with the valence band maxima at -6.93 and -5.49 eV with respect to vacuum and the conduction band minima at -5.62 and -4.60 eV with respect to vacuum for CH3NH3NiCl3 and CH3NH3NiI3, respectively. This work provides a pathway to explore new hybrid A+B2+X3--type semiconductor materials.

Ta2O5is a wide-bandgap semiconductor that offers interesting applications in micro-wave communications, mainly related to the manufacture of filters and resonators whosesize is inversely proportional to the dielectric constant of the material. For thatreason, in this work we present a theoretical study,based on density functional theory (using PBEsol and hybrid HSE06 exchange-correlation functionals),of the electronic and dielectric properties of the orthorhombic model -Ta2O5. We found that this model has a direct gap of2.09 and 3.7 eV with PBEsol and HSE06, respectively. Furthermore, the calculated static dielectric constant,51, is in good agreement with the reported values of other phases of this semiconductor.

Nb2O5 y Ta2O5 son óxidos semiconductores de brecha ancha, los cuales en los últimos años han despertado gran interés debido a sus múltiples aplicaciones tecnológicas, ya sea en electrónica, telecomunicaciones o fotocatálisis. Por estas razones, en este trabajo presentamos un estudio a partir de cálculos de primeros principios de las propiedades piezoeléctricas de las fases Z y β de Ta2O5, y de las fases Z y P de Nb2O5 utilizado la teoría de los funcionales de la densidad y la aproximación del gradiente, generalizado con la parametrización PBEsol. Una vez determinada la geometría de equilibrio para cada una de estas fases, realizamos un cálculo utilizando respuesta lineal para determinar el tensor piezoeléctrico asociado a cada una de estas fases, encontrando que la fase Z para ambos compuestos presenta una buena respuesta piezoeléctrica. Adicionalmente, encontramos que la fase β-Ta2O5 no presenta respuesta piezoeléctrica.

Nb2O5 and Ta2O5 are wide-bandgap semiconductor oxides that have attracted great interest in recent years due to their technological applications, such as in electronics, telecommunications or photocatalysis. Because of this, we present a study based on firstprinciples calculations of the piezoelectric properties of the Z and β phases of Ta2O5 as well as the Z and P phases of Nb2O5 by using the Density Functional Theory and the Generalized Gradient Approximation with PBEsol parameterization. Once the equilibrium geometry was determined for each of these phases, we made a calculation using the linear response theory to determine the piezoelectric tensor associated with each phase. We discovered that the Z phase of both compounds presents good piezoelectric response. Additionally, β-Ta2O5 does not show such response.

In recent years, organo-lead-halide perovskites have emerged as promising new materials for photovoltaics, reaching high efficiencies. The excellent photoelectronic properties and easy solution processing makes the lead perovskite an ideal light harvesting material in a solar cell. In spite of these great advantages, there are concerns about the lead contained in the material because of its well-known toxicity characteristics. Obtaining new metal halide perovskites without lead is still a challenge; until now, only a few experimental reports have been published and some other theoretical calculations replacing lead by most of the possible candidates of the periodic table. In this paper, we show for the first time synthesis of the calcium hybrid perovskites CH3NR3CaI3 andCH(3)NH(3)CaI(3-x)Cl(x) with complementary studies based on first-principles band structure calculation. Crystallographic analysis shows a pseudocubic structure, and optical measurements confirms that this type of perovskite absorbs light in the UV region, which is in good agreement with the calculation that showed a band gap larger than 3.5 eV.